The opposite of a double-blind trial. In open label trials, the effectiveness of a treatment is determined with full knowledge of whether or not the patient is taking the medication. Because the expectations of the investigator and patient can subtlely influence the results of such trials, they are considered less useful than double blind trials

An open-label trial or open trial is a type of clinical trial in which both the researchers and participants know which treatment is being administered. This contrasts with single blind and double blind experimental designs, where participants are not aware of what treatment they are receiving (researchers are also unaware in a double blind trial).